There are currently three prevalent types of wireless suspension used in the hard disk drive industry. They are Circuit Integrated Suspension (CIS), Flex on Suspension (FOS), and Integrated Lead Suspension (ILS). All differ in the manner in which they are fabricated. For the purpose of this disclosure and brevity, they will all be referred to as wireless suspensions. The embodiments in accordance with the disclosed invention are not limited by the manner in which the wireless suspension is fabricated.
The technologies used for terminating the wireless suspensions to the AE flex cable have been predominantly either solder re-flow, or ultrasonic (US) bonding. Solder re-flow technology has two approaches in use today. They are a right-angle fillet joint and a lap joint. In both approaches the wireless suspension termination pads and the AE flex cable termination pads are pre-coated, or tinned, with solder.
The fillet joint for solder termination technology relies on flattened solder pads to meet the flex cable pads at right angles. When heated the flattened solder pads of the wireless suspension become spherical and make contact with the flex cable solder pads, thus forming a right-angle fillet joint. The lap joint for solder termination technology involves the wireless suspension termination pads being exposed on all sides and overlapping the AE flex cable termination pads. Heat is applied to the wireless suspension pads and the tinned leads are fused together.
Ultrasonic termination technology is similar in design and configuration as lap joint solder re-flow technology. The primary difference is rather than being coated with solder, the wireless suspension and AE flex cable termination pads are plated, or coated with gold. The wireless suspension and AE cable termination pads are overlapped, pressed together and US energy is applied to fuse and join the termination pads.
The present invention recognizes a problem or a deficiency that arises from these termination methods. Specifically, these termination methods are detrimental to data rate. They also make it difficult to increase the number of terminations in the confined space allowed. In the case of the right-angle fillet joint, a large mound of solder results from the solder re-flow process thus creating undesirable capacitive coupling to adjacent fillet joints. Also, the pad size required to make an appropriate solder termination pad creates a discontinuity in the conductor width of the wireless suspension and the flex cable. Such discontinuities create reflection points for the data signals, which result in increased line impedance and degraded data rate performance. In the case of an overlapping joint, either solder re-flow or US, the pad size required to absorb assembly tolerances creates the aforementioned problem of discontinuity in the conductor widths. The large pad size also creates large amounts of solder, which creates a similar problem with the fillet joint of capacitive coupling.
There has been some effort to improve the right-angle fillet joint by making the fillet smaller and further spaced apart. The draw back to this is that a decrease in pad size places more challenge on the component manufacturers and assembly process. These challenges translate into higher cost due to lower yields both with components and assembly. These challenges become more difficult as the number of terminations per suspension become higher, which is the trend as the suspension is designed to allow more functions such as secondary actuation and thermally assisted fly-height control.